The long term goal of the proposal is to test the validity of selected DSM-III defined anxiety disorders by characterizing their pathophysiology. The measures of pathophysiology to be studied in this proposal are thought to reflect central noradrenergic function. Improved understanding of diagnosis and pathophysiology will contribute to the eventual development of improved treatment of these disorders. The specific aims of this proposal are: (a) to replicate the finding of blunted growth hormone (GH) response and enhanced 3-methoxy-4-hydroxy phenethyleneglyco (MHPG) response to clonidine in nondepressed patients with panic disorder; (b) to replicate the finding of blunted GH response to clonidine in nondepressed patients with obsessive-compulsive disorder; (c) to extend these same investigations to nondepressed patients with generalized anxiety disorder. Ten subjects in each of panic disorder, generalized anxiety disorder, obsessive-compulsive disorder and normal controls will be studied. The psychiatric groups will be defined by DSM-III criteria. All will be medically healthy, drug-free for at least three weeks, and on a low monoamine diet for at least three days prior to testing. On separate days, counterbalanced for order, each subject will receive, under single blind conditions, a placebo infusion and a clonidine infusion (2 ug/kg in 10 ml normal saline over 5 minutes). All will be hospitalized the night before the study and kept at bed rest except for bathroom use in order to minimized artifacts due to physical activity. An intravenous line will be put in place at 7 am the following day, 1 hour prior to intravenous challenge. Blood samples will be taken for GH and MHPG assay immediately before intravenous infusion and at 30, 45, 60, 90, 120 and 180 minutes thereafter. Blood pressure, pulse, and ratings of mood, anxiety, and clonidine side effects will be taken at each of these time points. GH will be measured by radioimmunoassay. MHPG will be measured by high pressure liquid chromatography. Analyses of variance, Scheffe tests and t-test will be the main tools for data analyses.